The present invention is directed to fluid couplings. More particularly, the present invention is directed to fluid couplings for coupling a reenforced hose to a metal tube wherein the couplings and hose are suitable for use in hydraulic vehicle brake systems.
As has been succinicly stated in U.S. Pat. No. 5,460,247 and reiterated here, there have been difficulties with brake hoses reinforced with braided wires. In order to accommodate necessary relative motion between the sprung and unsprung masses of a motor vehicle (i.e., the chassis and suspended wheels), suspension mounted hydraulic brakes are connected to the chassis by flexible hydraulic hoses. These hoses are typically fabricated form fabric braid reinforced elastomers.
Standard original equipment of such fabric reinforced flexible brake hoses for motor vehicles expand or swell to some extent under pressure, thus consuming available brake pedal travel which can result in a relatively xe2x80x9csoftxe2x80x9d feel to the brake pedal. This soft feel reduces the precision of brake modulation by the driver. These conditions are unacceptable in racing cars. For over 30 years, racing cars have been equipped with flexible brake hoses having a stainless steel braid layer over extruded Teflon. These hoses exhibit considerably less expansion under pressure resulting in higher and firmer brake pedal and a larger margin of safety because of more even friction pad wear and more precise brake modulation.
Despite an outstanding record of performance and reliability in racing and off-highway use, these high performance flexible brake hoses have not been certified for highway use because they have been unable to comply with the Basic Motor Vehicle Safety Standard 106, Section 56.3 (whip resistance test) set by the U.S. Department of Transportation (DOT).
Past efforts to substitute stainless steel braid protected Teflon flexible hose for the original equipment elastomeric brake hose on vehicles has usually led to fatigue failure of the protective braid at the end of the crimp or swedged collar or socket of the hose end fitting followed by fatigue failure of the Teflon hose and resultant loss of pressure. Consequently, there is a need for flexible brake hose assemblies that accommodate necessary relative motion between the chassis and wheels of a vehicle and passes all aspects of the whip resistance test required by the DOT.
One approach is to remove the stainless steel, braided reinforcement from the hose in the area of a metal coupling, but since the hose is made of polytetrafluoroethylene (PTFE), the hose tends not to meet thermal requirements when exposed to hot hydraulic fluid.
Hydraulic brake lines are one recognizable need for the invention, other needs arise when reinforced hoses are attached to other devices which may or may not be connected by tubes.
In view of the aforementioned considerations, the present invention is directed to a fluid coupling for coupling a hose to a device wherein the hose includes a deformable, resilient inner layer, a wire enforcement layer over the inner layer and an outer protective layer over the wire reenforcement layer. The fluid coupling comprises a fitting or xe2x80x9ceyeletxe2x80x9d having a first and a second portion; the first portion having a bore adapted to communicate with the device and a second portion having a projecting nipple for receipt in the hose, the eyelet further having an annular exterior groove therein. A crimping cup having first and second ends for mounting on the eyelet, wherein the crimping cup is disposed around the projecting nipple and initially has an inside diameter greater than the outside diameter of the hose. The crimping cup further has an inwardly projecting lip aligned with the exterior groove in the eyelet and a bell shaped pocket adapted to be disposed adjacent to an end portion of the hose which has been stripped of the outer layer. A coaxially strain relief element is disposed in the bell shaped pocket and is urged against the wire enforcement when the crimping cup is deformed radially inwardly to press the inner layer of the hose against the nipple and the inwardly projecting lip into the exterior groove in the tube fitting.
In accordance with one embodiment of the present invention, the coaxial strain relief element is an o-ring of resilient material, and in accordance with another embodiment of the invention, the coaxially strain relief is an annular ring having contoured exterior surface with a bulge received in the pocket of bell shaped end and a portion adapted to extend over the outer layer of the hose.
In accordance with a further embodiment of the invention, the fluid coupling is a coupling for coupling a hydraulic brake hose having a braided wire reenforcement layer to a metal tube.